Method of augmenting flow in a wastewater treatment plant

ABSTRACT

A wastewater treatment apparatus is provided which includes at least an aeration chamber and a clarification chamber having a common wall therebetween, a transfer port opening through the common wall between a lower portion of the clarification chamber and the aeration chamber, an aerator mechanism in the aeration chamber for creating wastewater flow currents which flow through an inlet portion of a flow augmenting device located in the common wall above the transfer port. The flow augmenting device is a conduit or pipe having a discharge outlet adjacent the lower portion of the clarification chamber through which exits the flow from the aeration chamber resulting in solid particles being agitated and returned from the clarification chamber lower portion into the aeration chamber through the transfer port.

This application is a division of application Ser. No. 08/399,935, filedMar. 6, 1995, now U.S. Pat. No. 5,569,376.

BACKGROUND OF THE INVENTION

This invention is an improvement in wastewater treatment plants,particularly wastewater treatment plants of the type disclosed in U.S.Pat. No. 5,207,896 granted on May 4, 1993 and U.S. Pat. No. 5,264,120granted on Nov. 23, 1993, each being in the name of Jan D. Graves, andeach being assigned to Norwalk Wastewater Equipment Co., of Norwalk,Ohio.

In wastewater treatment plants of the type disclosed in the aforesaidpatents, wastewater is introduced into a pretreatment chamber, flowsinto an aeration chamber, proceeds to a clarification chamber, flowsthrough the assignee's BIO-KINETIC® settling system and exits the latterthrough an effluent discharge pipe. A transfer port is provided at thebottom of a common wall between the aeration chamber and theclarification chamber. Activated sludge settles in a lower portion ofthe clarification chamber adjacent the transfer port and transienthydraulic currents created in the aeration chamber by for example, arotating aerator having a plurality of aeration nozzles or aspiratorports, lightly agitate the solids settled in the clarification chamberand they are, in part, mixed into suspension and carried back to theaeration chamber through the transfer ports by these transient hydrauliccurrents. These transient hydraulic currents are somewhat random and areless than 100% effective at returning settled sludge from the lowerportion of the clarification chamber back to the aeration chamber.

Settled sludge is made up of micro-organisms which accomplish thereduction of biological material in the aeration chamber, and it isessential to effectively return them to the aeration chamber. Therefore,having a less than a 100% effective return of the sludge from theclarification chamber to the aeration chamber is not advantageous formany reasons, most notable of which is that these activated sludgesolids lose the benefit of being in suspension in the aeration chamberwhere they obtain the food and oxygen necessary to sustain themselves.Hence, they die or change to a less desirable form. Deprived of oxygenand their normal food source these micro-organisms are subject to otherundesirable biological processes. These will naturally occur and cancause a degradation in effluent quality and reduce the efficiency of theoverall system in removing pollutants.

As another negative side effect of accumulated sludge in the lowerportion of the clarification chamber, it is first noted that aerationaccomplishes oxidation of nitrogen as a concurrent but separate stepwith carbonaceous (organic) oxidation. The oxidized nitrogen (nitrates)remains in the sludge and in solution, but when the activated sludge isallowed to accumulate in the bottom of a clarification chamber for asufficient time, the dissolved oxygen is consumed and themicro-organisms turn to the nitrate-bound oxygen to breathe. Thisreleases the nitrogen from the nitrate molecule and allows it to formgas bubbles which disperse throughout the "floc" causing it to becomebuoyant. Once sufficiently buoyant a clump or chunk of the floc willbreak loose from the sludge layer and float to the surface. This processof creating a bulking of buoyant sludge due to entrapped nitrogen gasbubbles is often referred to as denitrification. The sludge may remainat the surface for a time until further biological processes break itdown or the minimal hydraulic currents in the clarification chamberbreak it up and the gas bubbles are released into the free air. However,while floating on the surface this sludge does not receive sufficientoxygen or food to stay healthy, and it is not returned to the aerationchamber to perform additional biological reduction. The sludge may washout of the wastewater plant or plug downstream filters and/or settlingplates, such as in the BIO-KINETIC® system heretofore noted. Hence, itis extremely advantageous to preclude the formation of sludge "bulk" or"float."

SUMMARY OF THE INVENTION

In keeping with the foregoing, a primary object of the present inventionis to provide a device for augmenting wastewater flow between theclarification chamber and the aeration chamber to accomplish at leastthe following major functions substantially simultaneously:

1. A positive return of settled sludge from a lower portion of theclarification chamber into the aeration chamber.

2. Settled sludge that has accumulated on side walls of theclarification chamber is loosened thereby preventing a sludge build-upwhich would have the same negative effects as a lack of return of solidsfrom the clarification chamber into the aeration chamber.

3. Particles driven into suspension and kept sheared by the mechanics ofthe aeration chamber achieve a high degree of flocculation andsubsequently settle better when passing through the BIO-KINETIC®filtering/settling device.

4. The gentle mixing of the sludge at a lower portion of theclarification chamber strips small gas bubbles from entrapment withinthe floc particles without being intense enough to mechanically shearthe floc which allows the floc to settle in the lower portion of theclarification chamber and be returned to the aeration chamber to therebyessentially preclude sludge bulking due to denitrification.

Primarily, the latter functional advantages are achieved by the novelflow augmenting device of the present invention through the utilizationof a pipe or conduit having an inlet end portion opening into an upperportion of the aeration chamber and an outlet end portion adjacent theclarification chamber lower portion and the transfer port in the commonwall between the aeration and clarification chambers. Hydraulic currentsare created in the aeration chamber by a conventional aerator and assurface hydraulic currents radiate from the aerator they are directedinto the inlet end portion of the flow augmenting device, flow down amedial portion thereof and exit the outlet end portion adjacent thetransfer port at the lower portion of the clarification chamber. Thesecurrents then create sufficient turbulence to agitate suspend, and/orre-suspend settled sludge material in the clarification chamber lowerportion and return the suspended sludge material from the clarificationchamber lower portion through the transfer port to the aeration chamber.

Secondly, the currents created in the clarification chamber by the flowexiting the outlet end portion of the flow augmenting device inducegentle, vertical circular hydraulic currents in the clarificationchamber. These vertical circular currents loosen settled sludge frominner surfaces of the walls of the clarification chamber and keep sludgefrom thereupon in large quantities. Activated sludge, by its nature, hasa tendency to cling to the surfaces of a totally quiescent clarificationchamber, and traditionally larger wastewater treatment plants usemechanical mechanisms to "scrape" the walls of the clarification chamberto inhibit this accumulation. Such mechanical scraping mechanisms areentirely eliminated by the present invention, along with costs incidentto the operation and maintenance thereof.

Thirdly, as floc particles are transferred to the clarification chamberfrom the aeration chamber by hydraulic displacement, they tend to bevery small, almost discrete particles. Even though technically they are"floc," they have been agitated and mechanically sheared by the actionof the aerator of the aeration chamber. Since settling in theclarification chamber is by gravity, the smaller the particle the lesseffective it settles and separates from the surrounding liquid. Manylarger wastewater treatment plants use specifically designedflocculation chambers which gently stir the mixture allowing increasedparticle contact in a low shear environment. This allows the contact ofthe small particles with each other. Their natural adhesion causes themto coalesce into larger particles which settle better. It also providescontact and therefore adhesion of the floc to discrete particles whichwould not otherwise flocculate by themselves. Therefore, removalefficiency and overall process efficiency is increased.

Lastly, the hydro-mechanical action created by the flow augmentingdevice strips small bubbles, specifically entrapped nitrogen gas bubbles(denitrification) entrapped within the flocced particles, without beingintense enough to mechanical shear the floc. When these bubbles arereleased from the floc the floc can then properly settle in the lowerportion of the clarification chamber and be returned to the aerationchamber through the transfer port for subsequent processing. Thus sludgebulking is minimized due to nitrification with attendant increase inprocess efficiency while minimizing operational problems.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims and theseveral views illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of a novel wastewatertreatment plant constructed in accordance with this invention andillustrates pretreatment, aeration and final clarification chambers, aBIO-KINETIC® filtering/settling mechanism in the clarification chamber,a wall common to the aeration and clarification chambers, and a devicefor augmenting flow of wastewater from an upper area of the aerationchamber into a lower portion of the clarification chamber to createhydraulic currents effective for returning sludge settled in the lowerportion of the clarification chamber back to the aeration chamberthrough a transfer port of the common wall.

FIG. 2 is an enlarged fragmentary longitudinal sectional view takenthrough the aeration and clarification chambers and particularly thecommon wall thereof, and illustrates the longitudinal cross sectionalconfiguration of the wastewater flow augmenting device including arelatively large inlet end portion thereof, an outlet end portion whichdirects wastewater toward a lower portion of the clarification chamberto prevent sludge from settling thereat and/or agitating settled solidsback into suspension for ultimate transfer through the transfer portinto the aeration chamber for subsequent processing.

FIG. 3 is an enlarged fragmentary view taken generally along line 3--3of FIG. 2, and illustrates details of the inlet end portion of the flowaugmenting device of the invention.

FIG. 4 is a cross sectional view taken generally along line 4--4 of FIG.2, and illustrates the generally polygonal cross sectional configurationof the inlet end portion of the flow augmenting device.

FIG. 5 is a cross sectional view taken generally along line 5--5 of FIG.2, and illustrates the generally polygonal configuration of a medialportion of the flow augmenting device with one of a pair ofsubstantially parallel walls opening concavely outwardly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The novel method and apparatus disclosed specifically herein includesimprovements in the wastewater treatment plant disclosed in theaforementioned patents in the name of Jan D. Graves, and the totality ofthe disclosures of these patents are incorporated herein by reference.

In keeping with the present invention a novel wastewater treatment plantor apparatus is generally designated by the reference numeral 10(FIG. 1) and is normally designed for use with individual homes,although the same is readily adapted to many other facilities and isdesigned to utilize the well known digestion processes of wastewater orlike fluid treatment.

The wastewater treatment plant 10 includes an upper concrete casting 11and a lower concrete casting 12. A wall 13 is common to and separates apretreatment chamber 14 from an aeration chamber 15. Another wall 16 iscommon to and separates a clarification chamber 17 from the aerationchamber 15.

Wastewater W from a suitable source (not shown) enters the pre-treatmentchamber 14 through an inlet pipe 20 and flows beyond a depending bafflewall 21 through a transfer port 22 and a pipe or conduit 23 into theaeration chamber 15 via an outlet 24.

A pair of stacked concrete cylindrical risers 25,26 are supported by atop wall 27 of the upper casting 11, and the cylindrical riser 26 isclosed by a concrete cover 28 which includes a conventional fresh airvent assembly 30. An aerator mechanism 31 is conventionally supportedfrom the cylindrical riser 25 and includes a motor 32 which rotates anaerator shaft 33 having a plurality of aeration nozzles 34 from whichair bubbles exit to effect extended aeration of the wastewater W withinthe aeration chamber 15. The rotation of the aerator 33 and the airexiting the nozzles 34 create aeration chamber wastewater currents Cwhich, along an upper surface U of the wastewater W in the aerationchamber 15, travel generally radially away from the aerator 33.

Within the clarification chamber 17 there is located a BIO-KINETIC®filtering/settling mechanism, which is generally designated by thereference numeral 40, into and through which wastewater or effluentflows, particulate material is filtered or settled-out, and eventuallythe fully treated effluent discharges from the wastewater plant 10through an effluent discharge pipe or line 41. The filtering/settlingmechanism 40 is suspendingly supported from the top wall 27 of the uppercasting 11 and access thereto is provided by two removable cylindricalconcrete castings 42,43, the latter of which is closed by a removableconcrete cover casting 44. Chlorination and dechlorination tablets arehoused in respective chlorination and dechlorination tubes 45,46 fortreating the effluent during its flow through the mechanism 40 and priorto exiting the effluent discharge pipe 41.

The clarification chamber 17 includes a lower chamber portion 50 definedby the common wall 16, a tapering end wall 51 and opposite spacedtapering side walls of which only one of the tapering side walls 52 isillustrated. However, the walls 16, 51 and 52 generally define with aminor portion (unnumbered) of a bottom wall 54 the lower clarificationchamber portion 50 in which solids S tend to settle or accumulateadjacent a transfer port 55 of the common wall 16 which places theaeration and clarification chambers in fluid communication with eachother.

Absent a novel wastewater flow augmenting device 60 of the presentinvention, the solids or particles S settle by gravity adjacent thetransfer port 55 as settled sludge within the lower portion 50 of theclarification chamber 17 and tend not to flow through the transfer port55 back into the aeration chamber 15 with the resultant disadvantagesheretofore noted. However, in keeping with the present invention thewastewaster flow augmenting device 60 creates hydraulic flow currents C'which gently agitate the solids S precluding the accumulation of sludgeand reintroduce the solids S into the aeration chamber 15 through thetransfer port 55.

The wastewater flow augmenting device 60 is essentially a conduit orpipe which, as is best illustrated in FIG. 2, includes an inlet endportion 61, a medial portion 62 and an outlet end portion 63 having anoutlet 64.

The inlet end portion 61 of the flow augmenting device includes agenerally polygonal inlet opening 65 defined by an upper wall 66, alower wall 67 and opposite side walls 68,69. The walls 66,67 merge withrespective walls 71,72 whereas the walls 68,69 merge with identicalopposite walls 73,74 (See FIGS. 3 and 4). The walls 71-74 converge inthe direction of wastewater flow which in FIG. 2 is left-to-right. Thewalls 71-74 of the inlet portion 61 merge with respective walls 81-84(FIGS. 3-5) of the medial portion 62 and the outlet end portion 63.Though the entirety of the flow augmenting device 60 is of a generalpolygonal cross sectional configuration, the wall 81 is slightly curvedopening in a concave outward direction (See FIG. 5) to afford clearanceduring assembly, disassembly, servicing, etc. of the filtering/settlingmechanism 40 which is of cylindrical exterior configuration. In anactual structural embodiment of the invention the concave wall 81 isdefined by a 7.25" radius, the walls 83,84 are approximately 31/4" andthe wall 82 is 8", the measurements given being as the latter walls areviewed in FIG. 5 of the drawing.

OPERATION

As is best illustrated in FIG. 1, during the creation of the hydrauliccurrents C by the rotation of the aerator 33 and the air issuing fromthe nozzles 34, the surface currents C adjacent the upper surface U flowradially outwardly, as was described earlier and as is indicated by theupper series of wastewater flow arrows C of FIG. 1. This flow directs aportion of the wastewater W within the aeration chamber 15 into theinlet opening 65 and through the inlet end portion 61 of the wastewaterflow augmenting device 60, as is best illustrated in FIG. 2 by thewastewater flow arrows C associated therewith. This flow continues downthrough the medial portion 62 and the outlet end portion 63 eventuallyexiting the outlet 64 of the wastewater flow augmenting device 60resulting in the creation of the currents C' in the clarificationchamber lower portion 50 of the clarification chamber 17. The currentsC' form the numerous major functions described earlier including, ofcourse, the agitation of the settled solids or sludge S and/or themixture/agitation of the latter are creating unsettled solids insuspension which are carried back to the aeration chamber 15 through thetransfer port 55, again as indicated by the arrows illustrating the flowdirection from right-to-left in FIG. 2, for continued circulation by thecurrent C therein. Thus, even though the wastewater flow augmentingdevice or flow augmentation device 60 is totally passive in its designand function in that it has no moving parts, the hydraulic currents Ccreated in the aeration chamber 15 assure that any settled activatedsludge in the clarification chamber lower portion 50 will be returned tothe aeration chamber 15 strictly through the utilization of thegenerated aeration chamber hydraulic currents C. In other words, thehydraulic currents C created in the aeration chamber 15 are essentiallytransferred via the flow augmentation device 60 into the clarificationchamber 17 to create the currents C' therein with attendant transfer ofthe particles or solids S through the transfer port 55 into the aerationchamber 15.

The currents C' also "scour" the inner surfaces of the walls 16, 51 and52 to loosen accumulated settled sludge thereon in order to allow thelatter to drift to the clarification chamber bottom portion or lowerportion 50 for eventual return to the aeration chamber 15 by thecurrents C'. The latter avoids the attendant necessity and associatedcost of mechanical scrapers now utilized in the industry, and does so inan essentially maintenance free fashion. Since mechanical scrapers andother conventional mechanical sludge return devices are not utilizedwith the clarification chamber 15, hydraulic currents associated withthe latter which are detrimental to clarification functions are totallyavoided.

It is also important to note that due to the relatively larger crosssectional configuration of the inlet end portion 61 as compared to themedial portion 62 and the outlet end portion 63 of the flow augmentingdevice 60, the velocity and therefore the effectiveness of the hydraulicaction is increased by virtue of the Venturi effect. Thus the increasein velocity of the current flow C exiting the opening 64 assuresrequisite agitation of the sludge S through gentle hydro-mechanicalaction for sludge loosening and/or return which is best for flocpreservation and minimizing floc shear. In addition, locating thedischarge opening 64 of the flow augmenting device 60 adjacent thebottom wall 54 of the lower portion 50 of the clarification chamber 17prevents short-circuiting of the hydraulic flow path and thus assuresthat the currents C' essentially continuously and uninterruptedly flowfrom the clarification lower portion 50 through the transfer port 55into the aeration chamber 15 and eventually co-mingling with the flowcurrents C.

Another advantage of the flow augmenting device 60 is that larger flocparticles formed in the aeration chamber 15 are carried to the bottomportion 50 of the clarification chamber 17 as opposed to being directedagainst the filtering/settling mechanism 40 at the upper surface U ofthe wastewater W within the clarification chamber 17, as would occur inthe absence of the flow augmenting device 60. This effectively reducesfilter/settlement "loading" of the mechanism 40 and increases theefficiency of the filtration/settlement operation thereof. This resultsin less cleaning and downtime of the system and optimum effluent atdischarge.

Since the wastewater flow augmenting device 60 functions strictly independence upon the aeration currents C, the wastewater flow augmentingdevice 60 is automatically demand controlled. If the wastewater orbiomass in the aeration chamber 15 grows in volume, the operationaladjustment recommended for proper control would be to increase the runtime of the aerator mechanism 31, and additional biomass in the aerationchamber 15 would also result in increased settled sludge in theclarification chamber 17, both in the lower portion 50 and upon thewalls 16, 51 and 52 thereof. With the additional increase in runningtime there is a corresponding increase in the total flow through thewastewater flow augmenting device 60 which results in (a) an increase inthe return of settled sludge or solids S to the aeration chamber 15 fromthe clarification chamber 17 via the transfer port 55, (b) additionalscouring of the walls 16, 51 and 52 by the hydraulic currents C' and (c)additional flocculation time.

Apart from an increase in run time, the wastewater treatment plant 10normally operates in a cyclical fashion with the aerator mechanism 31operating during an "on" cycle and being cut-off during an "off" cycle.During such an "off" cycle there are more opportunities for the flocparticles to contact each other and to contact discrete particles. Thisaids in "polishing" the biomass. Additionally, each time theflocculation process is cycled, the floc undergoes alternateflocculation and settling and such intermittent settling provides moreopportunities for the floc particles to contact each other and tocontact discrete particles, again aiding in the polishing of the liquid.During the "on" cycle the currents C' created by the wastewater flowaugmenting device 60 inherently augment this polishing action throughthe continuous agitation of the particles S.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined in the appended claims.

I claim:
 1. A method of treating wastewater comprising the steps ofproviding a first chamber adapted to receive wastewater, a secondchamber also adapted to receive wastewater, a common wall between thefirst and second chambers, the second chamber including a lowermostchamber portion in which sludge is adapted to settle, a lowermostopening in a lowermost portion of the common wall being in immediate anddirect fluid communication with a lowermost chamber portion of the firstchamber and with the second chamber lowermost chamber portion;transferring sludge from the second chamber lowermost chamber portioninto the first chamber lowermost chamber portion through the lowermostopening, conducting wastewater from an uppermost water portion of thewastewater in the first chamber into the second chamber adjacent anuppermost portion of the second chamber, and thereafter continuingconducting the wastewater from the second chamber uppermost portiondownwardly into the second chamber lowermost chamber portion to createwastewater current flow augmenting the transfer of the sludge from thesecond chamber lowermost chamber portion into the first chamberlowermost chamber portion through the common wall lowermost opening bycontinuous recirculating flow.
 2. The wastewater treating method asdefined in claim 1 including the step of aerating and clarifying thewastewater in the respective first and second chambers.